Not Applicable
Not Applicable
1. Technical Field
The invention generally relates to receptacles and to the end wall structure of a container such as a metal can, bottle, or jar. More specifically, as applied to a metal can, the invention relates to the joint or seam between the sidewall and end wall of a metal can. As applied to a glass bottle, the invention relates to the side wall or skirt of a crown style bottle cap. As applied to a glass jar with threaded engagement to a lid, the invention relates to the side wall or threaded wall of a jar lid. The invention also relates to method and apparatus for forming the wall structure. The invention discloses several embodiments of a contoured lid or shell, especially a lid of variable thickness. In four specific embodiments, the invention discloses a multi-layer lid structure, a single layer lid structure with reduced thickness in the curl or peripheral lip portion, a crown style bottle cap with reduced thickness in the skirt portion, and a jar lid with reduced thickness in the shirt portion. In addition, the invention discloses apparatus and method for forming lids with a peripheral lip, curl, or skirt of reduced thickness.
2. Background Art
Metal containers are produced in two-piece and three-piece constructions. Three-piece containers are constructed from a cylindrical sidewall piece and two independent end wall pieces. The latter are applied to the respective ends of the sidewall to form a closed container. Two-piece containers are constructed from a single can body piece that includes both an integral sidewall and end wall, plus one end wall piece that is applied to the open end of the body to form a closed container. Both types of containers are produced in extremely large numbers, which creates an economic incentive to save even small amounts of metal in producing each one.
The manufacture of two-piece containers such as metallic beverage cans by the draw and iron process is widely practiced. The body of a two-piece container is efficiently produced from a single disc of sheet stock. For efficient use of metal, the thickness of the sheet stock is chosen with consideration for the maximum needed wall thickness, since most metal working processes reduce wall thickness rather than increase it. According to this known technique, sheet metal coil stock of the chosen thickness is fed into a machine called a cupper. There, the sheet is blanked into round discs of metal. After these discs are cut, the cupper processes the discs by forming them into shallow cups, which are substantially wider in diameter than the finished can body. The cup is further processed in a bodymaker machine. Here, a punch pushes each cup through a series of dies. The first die is a redraw die that reduces the diameter of the cup to the eventual diameter of the finished can body. Subsequent dies draw and iron the side walls of the can body, extending them to increased height, generally greater than the finished height of the can. At the termination of the punch""s stroke, the punch engages a doming die that configures the bottom wall or closed end of the can body. The opposite, open end of the can body is quite irregular after bodymaking and, thus, the can body is further processed in a trimming machine. There, the irregular wall of the open end is trimmed off, leaving behind a can body of standard dimensions and with a finished lip at its open end. After trimming, the lip is necked-in and flanged as preparation to receive the can lid. The can body is filled with its intended contents, after which the can body is closed by applying the lid to the flanged lip and seaming the edge of the lid to the flanged lip.
Container ends or lids have been formed in a variety of cross-sectional shapes and by a variety of methods that typically share a basic scheme. Metal sheet stock of a preselected thickness, such as 0.009-inches, is placed in a shell press between shearing dies that come together to shear the edge of a blank in the resulting shape of a disc. The sheet metal stock is chosen to be as thin as possible, with consideration for needed strength to resist pressure in the assembled can. Aluminum having a thickness of 0.009-inches is approximately the thinnest stock that can be used in a can that will hold a pressurized beverage such as a soft drink or beer. The thickness of the stock is substantially the same as the thickness of the blank, and the lid formed from the blank similarly is of approximately the same thickness as the original sheet stock.
After the blank has been formed, and typically within the same cupper or shell press used to shear the blank from sheet stock, a punch having a ring configuration is applied against the blank, producing a circular lid with a countersink or groove near its periphery and with an upstanding frustoconical wall or chuckwall rising from the outer edge of the groove. Other portions of the punch apparatus in the shell press form a peripheral flange extending outwardly from the top of the chuckwall. In a further step, the peripheral flange is formed into a downwardly curled or hooked shape that is better suited to mate with the lip of a container body. The lid is applied over a flanged top edge of a container body as mentioned above, and the peripheral curled wall of the lid is seamed to the top edge of the container body to form a seal.
Various methods of strengthening a lid are known, which typically enable a small amount of metal savings by reducing the necessary thickness of the lid. The process of reworking the countersink to deepen it and sharpen its curvature was found to increase the strength of the lid. Such reworking might draw the metal of the lid and thus thin it. U.S. Pat. No. 4,109,599 to Schultz taught that such drawing was undesirable and would reduce the pressure resistant capabilities of the lid. Thus, Schultz developed a method of reworking the countersink without drawing the metal. In fact, Schultz was able to slightly increase the thickness of metal in the countersink groove.
As shown by the following example patents, additional technologies have followed this approach of reworking the countersink or nearby structures to strengthen the lid. U.S. Pat. No. 4,606,472 to Taube et al. provides another method for reworking the countersink groove to increase metal thickness to form a strengthened lid and countersink. U.S. Pat. No. 6,065,634 to Brifcani et al. shows a lid configured in the traditional form with center panel, surrounding countersink wall, and chuck wall. The chuck wall is reworked for greater pressure resistance by extending it at a specified inclination that improves the closeness of the side wall to the lip of the container body. U.S. Pat. No. 5,950,858 to Sergeant strengthens the lid by forming an upward fold either surrounding the central panel or at the bottom of the depending countersink wall. U.S. Pat. No. 4,832,223 to Kalenak et al. teaches the use of coining to form a frustoconical surface at the junction of the central lid panel and the countersink wall for increasing strength of the lid. U.S. Pat. No. 4,809,861 to Wilkinson et al. strengthens the countersink wall by employing curves of several different radii. U.S. Pat. No. 4,333,582 to Bloeck et al. adds a stiffening groove that surrounds a pour outlet of a lid. This added groove allows the lid material to be thinner. The various modifications to the lid made in these patents appear to have helped save metal.
An asymmetric thinning technique is used in U.S. Pat. No. 5,152,421 to Krause. A blank is thinned by rolling portions of the blank to leave only a diametric central spine or belt of the original thickness to support a pull ring opener. Such asymmetric processing may produce irregularly shaped lids that would be difficult to apply and seal with standard equipment.
It would be desirable to reduce the thickness of the metal or other material of construction in a lid at selected locations where material thickness is not critical to the strength and pressure resistance of the lid. By such a selective thickness reduction, the technologies mentioned above could be applied as a supplemental means of strengthening the lid, particularly in regions of the lid where such thinning is not done. Thus, known technologies for strengthening the countersink, configuring the chuck wall, or forming strengthening structures on the central panel could remain useful.
Additionally, it would be desirable to employ an exceptionally thin sheet stock in the shell press in order to produce lids having such thin gauge at substantially any desired area. However, exceptionally thin stock, such as stock below about 0.009-inches, has been found to lack the needed strength to resist deforming when the can must contain a pressurized liquid. Deformation in the lid can produce a leaking can, leading to a spoiled product. Consequently, in order to successfully use exceptionally thin sheet stock, such as sheet stock below about 0.009-inches, it would be desirable to supplement the thin stock with an additional layer of reinforcing stock, placed only in those areas critical to maintaining strength in the lid and resisting reversal.
Metal containers such as beverage cans and lids are formed at sequentially arranged work stations, often by a series of machines arranged to form a xe2x80x9ccan line.xe2x80x9d Each of the various machines in the can line performs one or more forming steps. At the conclusion of each station""s function, the workpiece is conveyed to the next work station, which perhaps is located in the next sequentially arranged machine, until forming is complete. The space available for the can line is limited in any factory. Saving space is important. Therefore, it is desirable to perform multiple forming steps within a single machine and at each single work station. Particularly when a new forming step is introduced, it is desirable to perform the new step within the physical spaced allocated to the prior type of forming equipment. This enables a factory to incorporate the new step into the can line with only limited modifications to the can line, such as by changing the tooling within a single machine or substituting one machine for another. For thinning the lip of a container lid, it would be desirable to create both apparatus and method that can be performed within a single machine and preferably at a single work station.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the improved lid and method of this invention may comprise the following.
Against the described background, it is therefore a general object of the invention to provide an improved container end in which material savings are achieved by annular, concentric thinning of the peripheral lip, curl wall, or skirt.
Another general object of the invention is to provide a method and apparatus for forming a container end having an annular, concentric, thinned peripheral lip, curl wall, or skirt.
Additional objects, advantages and novel features of the invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by the practice of the invention. The object and the advantages of the invention may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims.
According to a first aspect of the invention, a container lid is formed by a method that produces a thinned peripheral lip. First, according to a blanking step, a blank is sheared from planar sheet stock of generally predetermined stock thickness. The blank is composed of at least a central portion and a peripheral annular lip portion circumferentially bounding the central portion and lying generally in a plane. Second, according to a clamping step, the peripheral annular lip portion is clamped between first and second clamping elements, one against each face of the blank. At least the first clamping element carries a thinning tool for thinning a peripheral lip of the blank. Third, according to an ironing step, the central portion of the blank is displaced from the plane of the peripheral lip portion while applying through the clamping elements a predetermined clamping force of a magnitude allowing movement between the peripheral lip portion and the thinning tool, with resultant thinning of the lip portion to less than the generally predetermined stock thickness.
Optionally, the method may include an additional step, after the second step and before the third step, in which a transverse wall is formed by applying a center forming die against one side of the central portion of the blank. Thereafter, the third step is performed by moving the first and second clamping elements in unison to push the central portion of the blank against the center forming die, deforming the blank at the outer margin of the central portion to form an annular wall, which extends transversely to the central portion.
Optionally, the method may employ a center forming die that is configured with a central cavity bounded by a peripheral shoulder that first contacts the central portion of the blank in the transverse wall forming step. Then, according to a fourth step, a countersink element that is sized to fit into the central cavity of the center forming die is applied against the central portion of the blank on the side opposite from the center forming die.
Optionally, according to a fifth step, a central wall is formed by forming the blank over the peripheral shoulder of the center forming die by moving the countersink element further toward the central cavity, while simultaneously performing a further thinning step by further drawing the peripheral lip over the thinning tool and simultaneously forming an annular groove into the blank at a location spaced from the sheared edge of the blank. These steps define a container lid having a disc-shaped planar central wall circumferentially bounded by a concentric annular groove, in turn circumferentially bounded by a concentric annular wall positioned transversely to said planar central wall.
Optionally, a releasing step is performed by separating the first and second clamping elements.
Optionally, a stripping step is performed by moving one of the clamping elements to push the container lid free of the center forming die.
According to another aspect of the invention, an improved container end has a disc shaped central wall, circumferentially bounded by a concentric annular groove, in turn circumferentially bounded by a concentric annular frustoconical wall, in turn circumferentially bounded by a concentric annular peripheral wall. The improvement provides a central wall and countersink groove configured with a thickness greater than a predefined minimum dimension; and the peripheral wall is configured with a thickness less than the predefined minimum dimension.
In an optional aspect, the frustoconical wall is configured with a thickness greater than the predefined minimum dimension at least over an annular portion immediately juxtaposed to the groove. In another optional aspect, the frustoconical wall is configured to have a thickness less than 60% of the predefined minimum dimension at least over an annular portion immediately juxtaposed to the curl wall. In a further optional aspect, the curl wall is configured with a thickness no greater than about 56% of the predefined minimum dimension.
One method of achieving these reductions in material thickness is the use of a central wall composed of a laminate formed of at least two sheets of forming material; and the curl wall is formed of at least one less sheet of forming material than the laminate of the central wall. More specifically, the central wall may be formed of first and second sheets of forming material; while the curl wall is formed of a peripheral portion of only the first sheet of forming material. Each sheet of the laminate material may be of a thickness less than the predetermined minimum thickness. The central wall, annular groove, and frustoconical wall each may be composed of a laminate formed of at least first and second sheets of forming material, in which the first sheet has a minimum thickness of less than 60% the thickness of the laminate; and the curl wall may be formed of a peripheral portion of the first sheet of forming material. The first and second sheets of forming material each may be formed of a metal, such as aluminum or steel.
According to another aspect of the invention, a container end is formed by a method in which, first, a disc-shaped blank is sheared from planar sheet stock of a predetermined stock thickness. Second, an annular groove is formed into the blank at a location spaced from the sheared edge of the blank, defining container end having a disc-shaped planar central wall that is circumferentially bounded by a concentric annular groove. In turn, the groove is circumferentially bounded by a concentric annular wall that is positioned transversely to the planar central wall. Third, the center portion of the container end is positioned on a supporting tool, and the annular wall is engaged with a thinning tool. Fourth, the thinning tool interacts with the annular wall for thinning the annular wall to a thickness less than the predetermined stock thickness.
Optionally, the fourth step may be performed by carrying the container end on a forming mandrel for longitudinal movement through at least one ironing die, thinning the annular wall to form a container end with an annular wall thickness less than the predetermined stock thickness. In another option, the fourth step may be performed by carrying the container end on the forming mandrel sequentially through two ironing dies. In a detailed aspect, the fourth step may be performed by reducing the thickness of the annular wall by more than 40% of the predetermined stock thickness. In a further option, the fourth step may be performed by spinning the forming mandrel with the container end carried on it, and applying a forming roll against the annular wall to thin the annular wall forming a container end with an annular wall thickness less than the predetermined stock thickness. Optionally, the fourth step is performed by moving the center of the container end with respect to the thinning tool, applying the thinning tool to thin the annular wall.
Another aspect of the invention provides an apparatus for forming a container lid with a thinned peripheral lip portion from a disc-shaped blank of preselected diameter, having a central portion and an annular, generally planar, peripheral lip portion, formed of a generally predetermined stock thickness. The apparatus is formed of a pair of opposed first and second annular clamping elements that are sized to engage the blank at the annular peripheral lip portion. A thinning means is carried by at least the first of the clamping elements for thining the peripheral lip portion of the blank by relative movement between the thinning means and the peripheral lip portion. A force selection device applies a preselected clamping force between the clamping elements in a degree permitting the peripheral lip portion to be drawn between the clamping elements in response to opposite relative movement between the central portion of the blank and the peripheral lip portion, transverse to the plane of the peripheral lip portion. A displacing device oppositely relatively moves the central portion of the blank and the peripheral lip portion, transversely to the plane of the peripheral lip portion, thinning the peripheral lip portion by relative movement between the thinning means and the peripheral lip portion.
The accompanying drawings, which are incorporated in and form a part of the specification illustrate preferred embodiments of the present invention, and together with the description, serve to explain the principles of the invention. In the drawings: